In the fabrication of hollow extruded items such as pipes or tubes which are produced from thermoplastic materials, it is desirable that the final products have a uniform wall thickness. Any uneven or thin spot in the wall of a plastic pipe makes the pipe not only structurally unsound but also gives the pipe varying flexibility over its length.
A conventional method for producing a bend in a plastic pipe involves heating the pipe in a liquid bath until the plastic reaches a temperature at which it becomes pliable. The pipe is then bent into the desired shape. A major drawback in this procedure is that the exterior wall surface is stretched and becomes significantly thinner while the interior wall surface of the bend is wrinkled and made uneven. A pipe produced in this manner not ony has structural weakness on the exterior surface, a situation further aggravated by the possibility of the pipe receiving abrasion in this area, but also produces uneven fluid flow through the pipe due to the wrinkles created on the interior wall of the bend.
Further methods for producing bends in plastic pipe are shown in U.S. Pat. No. 3,748,077 to Williams et al and U.S. Pat. No. 3,776,539 to Curtis et al. In the Williams patent a pivoted arm is connected to a pipe as it is received from an extruding die and the die drives the pivoted arm through an arc. The Curtis et al invention discloses a jig which clamps to a section of pipe for bending thereof. The Curtis disclosure does not show a continuous pipe feed.